Piston ring and piston device

Abstract

A piston ring which can sustain a superior effect of preventing aluminum cohesion for a long time in a high output engine is provided. At least one of the upper and lower side faces of a piston ring is coated with a polyimide film having hard particles dispersed therein. Employed as the hard particles may be alumina, zirconia, silicon carbide, silicon nitride, cubic boron nitride, or diamond. The hard particles are to be 0.01 to 5 μm in average particle diameter, and the film is 2 to 30 μm in thickness.

The invention claimed is: 
     
       1. A piston ring having at least one of upper and lower side faces coated with a film, wherein the film is a polyimide film containing hard particles,
 the hard particles have an average particle diameter of 0.01 to 5 μm, and 
 the film has a hardness HV at 250° C. of 30 to 70 which falls within a range of ±40% of a piston hardness at 250° C. 
 
     
     
       2. The piston ring according to  claim 1 , wherein the hard particles are of at least one type selected from the group consisting of alumina, zirconia, silicon carbide, silicon nitride, cubic boron nitride, and diamond. 
     
     
       3. The piston ring according to  claim 1 , wherein the film has a thickness of 2 to 30 μm. 
     
     
       4. The piston device having the piston ring according to  claim 1  mounted thereon. 
     
     
       5. The piston ring according to  claim 2 , wherein the film has a thickness of 2 to 30 μm. 
     
     
       6. The piston device having the piston ring according to  claim 2  mounted thereon. 
     
     
       7. The piston device having the piston ring according to  claim 3  mounted thereon.